This invention relates to a method of and apparatus for introducing a sample containing target components to be analyzed into a capillary column of a gas chromatograph through a vaporization chamber provided at the inlet of the column. Throughout herein words like "inject" and "injection" will be reserved for denoting the operation of causing a sample liquid from outside to be placed inside the vaporization chamber, and words like "introduce" and "introduction" will be used regarding the operation for transporting the sample inside the vaporization chamber into the column on a carrier gas flow.
As shown in FIG. 9A, a gas chromatograph usually has a vaporization chamber 10 at the inlet of a capillary column 22 and a septum 11 made, for example, of silicone rubber is placed at the top end of the vaporization chamber 10. A carrier gas flow route 23 for introducing a carrier gas (such as He) and a septum purge flow route 25 for removing gases generated from the septum 11 are connected to an upper part of the vaporization chamber 10. The carrier gas flow route 23 contains a pressure adjustor 24 by means of which the flow rate of the carrier gas being supplied into the vaporization chamber 10 can be controlled. The septum purge flow route 25 contains a pressure sensor 26 for detecting the pressure inside the vaporization chamber 10, as well as a flow resistor 27.
The vaporization chamber 10 is surrounded by a heater 12 and contains therein a tubular member (herein referred to as "the insert" 13) made, for example, of glass. A split flow route 28 containing an electromagnetic valve 29 is also connected to the vaporization chamber 10 for discharging the gas from the interior of the vaporization chamber 10. Prior to the injection of a sample, the pressure adjustor 24 is appropriately operated such that a carrier gas flows at a specified rate through the insert 13 inside the vaporization chamber 10 into the column 22. A needle 21 at the tip of a syringe 20 is then caused to penetrate the septum 11 and a sample liquid, normally consisting of target components to be analyzed and a solvent such as acetone and hexane, is injected.
For introducing the sample liquid injected into the vaporization chamber 10 further into the column 22 in a gas chromatograph as described above, there have been known several different methods such as the splitless method, the cold on-column method, and the programmed temperature vaporizer (PTV) method. In the splitless method, the heater 12 is controlled at a constant temperature such that the temperature inside the vaporization chamber 10 is maintained above the boiling points of the components to be analyzed and about 1-2 .mu.l of a sample liquid is injected from the syringe 20 into the vaporization chamber 10 while the electromagnetic valve 29 in the split flow route 28 is kept closed. Since the interior of the vaporization chamber 10 is at a high temperature, the injected sample liquid is vaporized, is carried by the flow of the carrier gas, passes through the insert 13 and is introduced into the column 22. As the vaporized solvent remaining in the vaporization chamber 10 flows into the column 22 slowly over an extended length of time, the tailing of the solvent peak appears prominently on the chromatogram. After a specified length of time has elapsed since the injection of the sample, the valve 29 is opened and the vaporized solvent inside the vaporization chamber 10 is discharged to the exterior through the split flow route 28.
In the splitless analysis, components with relatively low boiling points vaporize instantly but components with high boiling points may not vaporize as easily. For this reason, it has been known to insert a filler such as glass wool into the insert 13 such that even components with high boiling points can vaporize more quickly, heated by the filler, and are introduced into the column 22. Thus, all components to be analyzed can be dependably vaporized and the repeatability of the analysis improves.
Even if non-volatile components are present, such components are withheld inside the insert 13 (or by the filler) and are prevented from entering the column 22. Contamination of the column 22 can thus be avoided, and the advantage is that the user has only the insert 13 (or the filler) to exchange.
Since the interior of the vaporization chamber 10 is always maintained at a high temperature in the splitless analysis; however, components which can be decomposed easily by heat may undergo thermal decomposition before they are introduced into the column 22. If the insert 13 is filled with a filler, furthermore, there is the possibility that the target components to be analyzed may be adsorbed or caused to decompose thereby.
In the cold on-column method, an adaptor 131 as shown in FIG. 9B, made for example of stainless steel, is used instead of the insert 13 of FIG. 9A and is set inside the vaporization chamber 10, the internal temperature of which is made controllable according to a program. The column 22 is inserted into this adaptor 131 such that its top end is directly below the septum 11. While the heater 12 is controlled so as to maintain the interior of the vaporization chamber 10 at a temperature below the boiling point of the solvent for the sample liquid, about 1-2 .mu.l of the sample liquid is injected from the tip of the needle 21 directly into the column 22. The sample liquid thus injected is evaporated while passing through the column 22. By this method, therefore, the injected sample can be entirely introduced into the column 22 dependably without regard to the boiling points of its components. Since the vaporization chamber 10 is maintained at a low temperature, even those components which would decompose easily by heat can be introduced into the column 22 without undergoing thermal decomposition. If the sample liquid contains a non-volatile component, however, such a component pollutes the column 22 and a contaminated portion of the column 22 must be cut off. Since the sample liquid must be injected directly into the column 22 according to this method, furthermore, a special syringe 20 with needle 21 with a sufficiently small outer diameter must be used, and there is the danger of damaging the column 22.
In the PTV method, an insert 13 filled with a filler 132 as shown in FIG. 9C is usually used. The heater 12 is controlled such that the temperature inside the vaporization chamber 10 will be near the boiling point of the solvent when the sample is injected and will increase thereafter in a specified manner. At the time of the sample injection, the injected sample liquid is not completely vaporized because the temperature is relatively low and is temporarily held by the filler 132. As the temperature is raised, components are vaporized sequentially in the order of their boiling points and are transported by the flow of the carrier gas through the insert 13 into the column 22.
By this method, as by the splitless method, the valve 29 in the split flow route 28 must be opened after a certain length of time has elapsed such that the effect of the tailing of the solvent peak may be reduced. If this time is too long, the tailing of the solvent becomes too large. If this time is too short, the tailing can be made smaller, but some target components to be analyzed may be discharged to the exterior.
Each of the prior art methods described above has both advantages and disadvantages. Thus, when many components are analyzed at once by a single injection, some of the target components to be analyzed, such as those which decompose easily by heat and those with boiling points near that of the solvent, may not be appropriately introduced into the column 22 and may fail to be correctly analyzed.